How does a fingerprint reader work on a laptop?

Nothing is completely secure: locks can be picked, safes can be opened, and passwords can be guessed or tampered with. So how can we protect sensitive information on a laptop, for example? One way is to use biometric security methods such as the fingerprint reader that many laptops incorporate as standard, just like smartphones, and in this article we are going to tell you how they work, how and where your fingerprints are stored and why (almost) they never fail.

Not long ago, if you had been fingerprinted, it was probably because you were being accused of a crime; Now, however, it is one of the favorite methods to add a layer of security to our devices because they are a very reliable, simple and also cheap method.

Why are fingerprints unique?

It is quite obvious why we have fingerprints: the small friction ridges on the tips of our fingers make it easier for us to grasp the objects we want to grasp with our hand. By making the fingers rougher, these ridges increase the force of friction between our hands and the objects we hold, making it difficult for things to fall. You have fingerprints even before you are born, and in fact the fingerprints are fully formed when you’ve only been in the womb for 7 months. Unless you have accidents with your hands, your fingerprints will remain the same for life .

What makes fingerprints such a brilliant way of differentiating people is that they are virtually unique: fingerprints are developed through an essentially random process with your DNA code, and because the environment in the womb it also has its effect, even two twins have different fingerprints. While it is possible to find two people with virtually identical fingerprints, the chances of this happening are negligible.

Therefore, when fingerprints are used to control a person’s access to a computer system such as a laptop or smartphone, the chances of a random person having the correct fingerprint are generally so slim. which are almost ridiculous, far less than a person can guess your password or can break a physical block. Therefore, fingerprints are considered one of the best security systems out there.

How does a fingerprint reader work on a laptop?

Taking your fingerprints at a police station involves pressing your fingers on an ink pad and then rolling your fingers across a piece of paper to leave a clean impression on a sheet. The impressions are also stored digitally afterwards so that the police can verify if you have committed any known crimes or if you do so in the future (this is known as “being booked”).

But when fingerprints are used to control access to computer systems like a laptop, more sophisticated methods must be used: we must have a fingerprint reader that scans the surface of the finger quickly and then converts the scanned representation into a code that can be compared. with its database, that is, to allow access previously it is necessary that the fingerprint is already processed and stored.

There are three ways to scan the fingers. An optical scanner works by shining bright light onto your fingerprint and literally taking a photograph of it. If you’ve ever photocopied your hand, you’ll know exactly how this works, but instead of producing a dirty black photocopy, the image is fed into the PC’s scanner, which uses a light-sensitive microchip (be it a CCD, a charge-coupled device or a CMOS image sensor) to produce a digital image. The PC automatically analyzes the image, selecting just the fingerprint, and then uses sophisticated pattern-matching software to convert it into code.

Another type of scanner, known as a capacitive, measures your finger electrically. When the finger rests on a surface, the grooves of the prints touch the surface while the gaps between them are slightly outside of it. In other words, there are different distances between each part of the finger and the surface below, so the capacitive scanner creates an image of the fingerprint by measuring these distances; this type of scanner is a bit like the touch screens of mobile phones, although although they are faster than optical ones, they do not work well when the finger is not clean or is wet.

The third type of fingerprint reader is called an ultrasonic scanner because it uses high-frequency sound waves (ultrasound) to “map” your finger instead of using light like the previous two. This type of scanner can be integrated under touch screens, which is why it is used in some smartphone models, but its operation is similar to that of optical scanners for all purposes.

What happens during the fingerprint scan?

Unlike ordinary digital photos, scans must capture exactly the correct amount of detail (brightness and contrast) so that individual ridges and other details in the fingerprint can accurately match previously taken scans. Remember that fingerprints can be used as evidence in criminal trials, where a conviction could result in a long jail sentence; For this reason, quality control is surely the most important part of the fingerprint scanning process, and this applies equally to a laptop fingerprint reader.

This is how the scanning process works with a simple optical scanner (with the other two types it is similar but with the differences that we have explained in the previous section):

1. A row of LEDs scans the bright light onto the glass (or plastic) surface that you place your finger on (sometimes called a stage).
2. Image quality will vary depending on how you press, how clean or greasy your fingers are, how clean the scanning surface is, the ambient light level, etc.
3. The reflected light bounces off the finger through the glass to a CCD or CMOS image sensor.
4. The longer this image capture process takes, the brighter the image formed on the sensor will be.
5. If the image is too bright, areas of the fingerprint (including important details) may disappear completely, like a digital photo indoors where the flash is too close or too strong. If it is too dark, the image will appear black and the details will be invisible for the opposite reason.
6. An algorithm tests whether the image is too light or too dark; if so, an audible beep or LED indicator alerts the operator and the measurement needs to be repeated.
7. If the image is acceptable, another algorithm tests the level of detail, usually by counting the number of ridges and making sure there are alternating zones of light and dark (as would be expected from a decent footprint image). If the image fails this test, return to step 1.
8. As long as the image passes these two tests, the scanner accepts the image, which is stored as an acceptable scan on a laptop’s internal memory chip for this purpose. Typically, images captured this way are 512 x 512 pixels (the dimensions used by the FBI) ​​and the standard image is 2.5 cm (1 inch) square, with 500 dots per inch of resolution and 256 shades of gray.
9. Now the PC can store the image in its database (temporarily or indefinitely) and automatically compare it with the fingerprints that are approved to unlock the equipment and allow access.